Orion

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Orion, the Hunter, is a constellation lying on the celestial equator. It is one of the brightest and best known constellations in the sky. It is also one of the few constellations known since ancient times. Early Greek writers such as Homer and Hesiod made references to Orion in their works.

In Greek mythology, Orion was a hunter, son of the sea god Poseidon and the Cretan princess Euryale. It was said that Poseidon had given Orion the ability to walk on water. The constellation Orion is depicted as a man raising his club and shield, facing the charge of a bull, represented by the neighbouring constellation Taurus, and standing next to the river Eridanus. The tale that corresponds to this representation is not found in Greek mythology, however, but Sumerian one.

The Sumerians believed that the constellation, which they called Uru An-na ("light of heaven"), represented their hero Gilgamesh fighting the bull of heaven, Gud An-na, which corresponds to the constellation Taurus. Even though the Greek equivalent for Gilgamesh is Heracles, who was once given the task to catch the Cretan bull, and Ptolemy described the constellation known as Orion as a man with a club and lion's pelt (not unlike Heracles), there is no solid evidence of a connection between the constellation Orion and Heracles.

In the sky, Orion and his two dogs, represented by the constellations Canis Major and Canis Minor, are seen pursuing a hare, Lepus. In another tale, Orion fell in love with the Pleiades (a star cluster in Taurus), the seven daughters of Atlas and Pleione, and kept pursuing them until Zeus took them away and placed them among the stars, where Orion can still be seen following them across the sky.

The myth of Orion's death is linked to the constellation Scorpius, which lies on the opposite side of the sky. Orion was said to have boasted to the goddess Artemis and her mother Leto that he could defeat any animal on Earth. The Earth heard this and sent a scorpion, which stung Orion and killed him. For this reason, when the constellation Scorpius rises in the east, Orion disappears below the horizon in the west.

The constellation Orion carries great significance in many cultures. In Hungarian mythology, it is identified with Nimród, another great hunter and warrior, and the mythological father of the Hungarians. In the Indian Rig Veda, the constellation mentioned as Mriga ("the deer"). In Scandinavian myths, it was called Frigg’s Distaff, after the tool Frigg, the highest goddess of the Aesir, used for spinning. The Aztecs knew the belt and sword of Orion as the Fire Drill. When it appeared in the sky, it signalled the start of the New Fire ceremony, a ritual performed to postpone the end of the world. The Chinese called the constellation Shen, after another great hunter and warrior.

In the southern latitudes, Orion appears differently in the sky. In Australia and New Zealand, his belt and sword are known as the Pot or Saucepan. In South Africa, the three bright stars forming Orion's Belt are called Drie Konigs (Three Kings) or Drie Susters (Three Sisters). The belt was also called Driekoningen (Three Kings) is Dutch star charts in the 17th and 18th century. In South America, the three prominent stars are known as The Three Marys.

In the Late Bronze Age, the constellation was called The Heavenly Shepherd in Babylonian star charts. There are references to Orion in the Bible in the Book of Job and the Book of Amos. In ancient Egypt, the constellation was identified with Osiris, the god of rebirth and the underworld, and also sometimes associated with the Pharaoh Unas, the last ruler of the Fifth dynasty. After death, pharaohs were said to be transformed into Osiris, a god in the sky. The pyramids at Giza mirrored the pattern of the stars in Orion and the air shaft in the King's Chamber in the Great Pyramid was aligned with the star Alnitak, providing the king with the path to the heavens.

The constellation Orion occupies an area of 594 square degrees and contains three stars with known planets. It can be seen at latitudes between +85° and -75° and is best visible at 9 p.m. during the month of January. The constellation currently lies south of the ecliptic and will keep moving further south as a result of precession.

Orion contains some of the brightest stars in the sky. [5971] beta Orionis or Rigel ("the foot"), the brightest star in Orion, is the sixth brightest star in the sky. It is a blue supergiant located at Orion’s left foot. It is a very old star that will soon either become a supernova or shed its outer layers and turn into a white dwarf. It is approximately 800 light-years distant.

[5972] alpha Orionis or Betelgeuse ("the hand of the central one"), the second brightest star in the constellation, is also the twelfth brightest star in the sky. It is a massive red supergiant, another very old star that will soon explode into a supernova. Betelgeuse marks the right shoulder of Orion and is approximately 640 light-years distant. It is a variable star and occasionally appears brighter than [5971] Rigel.

[5973] gamma Orionis or Bellatrix ("the female warrior") is the 21st brightest star in the sky. It is a blue giant, an eruptive variable star, marking the hunter’s left shoulder. It is sometimes also known as the "Amazon star."

The three stars forming Orion’s belt are [5977] delta, [5974] epsilon and [5975] zeta Orionis. [5977] delta Orionis or Mintaka ("region") is an eclipsing binary variable star system that consists of a large blue giant and an O-type white star. It is approximately 900 light-years distant.

[5974] epsilon Orionis or Alnilam ("the string of pearls") is a blue-white supergiant, about four million years old. It is the central star of Orion’s belt and the 30th brightest star in the sky.

[5975] zeta Orionis or Alnitak ("the girdle") is a triple star with a hot blue supergiant, the brightest class O star in the sky, for a primary component. It is approximately 800 light-years distant.

[5976] kappa Orionis or Saiph ("the sword") marks Orion's right foot. It is a blue supergiant about 720 light-years distant.

[5978] iota Orionis, also known as Hatsya or Na’ir al Saif ("the bright one o the sword") marks the tip of Orion’s sword. It is a quadruple star system with a hot blue giant for a primary component.

[5985] sigma Orionis is another interesting multiple star system. The primary component is composed of a blue dwarf, one of the most luminous stars known, and a B-type dwarf. The other component is also composed of two dwarfs, both B-type. The last component is an A-type dwarf. Sigma Orionis is approximately 1,150 light-years distant.

[5981] lambda Orionis, also known as Meissa ("the shining one") and Heka ("a white spot"), is a binary star composed of a blue giant and a hot blue-white dwarf. Together with [5993] phi-1 and [5987] phi-2 Orionis, it forms a triangle that marks Orion’s head.

The most notable deep sky object in the constellation is the Orion Nebula (Messier 42), located under Orion's belt. It is a star-forming region with clouds of dust and gas.

The Orion Trapezium Cluster, or simply the Trapezium, is located in the centre of the Orion Nebula. It is an open cluster marked by an asterism of four stars, the brightest one of which is [6023] theta-1 Orionis C. The stars represent Orion’s sword, seen hanging from his belt.

IC 434 or the Horsehead Nebula appears as a dark cloud of thick dust in the shape of a horse’s head. The nebula is located near [5975] zeta Orionis.

Messier 43 or NGC 1982 is also known as De Mairan’s Nebula. It is one of the star-forming regions in the Orion Nebula, separated from the larger nebula by a large, turbulent black lane.

Messier 78 or NGC 2068 is a reflection nebula, originally catalogued as a comet-like object. It is the brightest diffuse reflection nebula in the Orion Complex.

Barnard’s Loop is an emission nebula in the shape of a loop that covers most of the constellation and appears to centre on the Orion Nebula. The loop is believed to have been created in a supernova explosion about two million years ago.

The Flame Nebula (NGC 2024) is another emission nebula. [5975] zeta Orionis shines ultraviolet light into the nebula’s clouds of hydrogen gas and the glow is the result of the recombined electrons and ionized hydrogen.

The nebulae in Orion are all part of the Orion Molecular Cloud Complex, one of the most active star-forming regions in the sky. The cloud is hundreds of light-years across in size and lies between 1,500 and 1,600 light-years away from Earth. It appears very bright in infrared wavelengths.